The present invention relates generally to radar systems, and more specifically to a light-activated modulator which modulates radar waves at microwave frequencies.
Modulators are used in microwave or millimeter-wave radars to turn off or turn on power sources or to amplitude modulate a signal. The conventional modulator may be a diode or tube in a waveguide. Such modulators receive a carrier frequency signal, from a microwave source which they modulate by an electronic modulating signal, from a waveform generator, to produce a modulated signal which is radiated out to detect objects in the radar's field of view.
The task of producing a light-activated modulator for radar systems, is alleviated to some extent by the systems disclosed in the following U.S. Patents, the disclosures of which are specifically incorporated herein by reference:
U.S. Pat. No. 3,222,601 issued to Sartorio;
U.S. Pat. No. 4,150,3S2 issued to King; and
U S Pat. No. 4,575,727 issued to Stern et al.
The Sartorio reference discloses an antenna beam scanner in which an antenna beam is scanned by selectively illuminating a layer of photoconductive material which is placed over the aperture of an antenna. The purpose of the Sartorio system is to vary the direction and/or shape of the radio frequency (RF) beam.
The King reference discloses an antenna system which provides electronically controlled scanning of the radiation pattern. This system uses an array of elements which are electrically connected to a set of phase shifters which electronically steer the radar beam.
The Stern et al reference discloses a millimeter-wave electronic scan phase array antenna. This system also steers its radar beam electronically by shifting the individual phases of RF signals across an array of transmitting radar elements.
While the systems disclosed in the above-cited references are instructive, most prior art systems appear to modulate their radar waves by either switching on and off their power sources, or by other electronic conventional methods such as amplitude modulation. In view of the foregoing discussion, it is apparent that there remains the need to provide a system capable of optically modulating radio frequency signals for both transmission and reception. The present invention is intended to satisfy that need.